A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
At present, in lithographic applications, two different types of motor configurations are used to move a substrate table (also identified as substrate stage) that is configured to hold the substrate.
A first type is disclosed in WO98/40791 A1 which is enclosed herewith in its entirety by reference. In this configuration, the substrate table is supported by a base plate, such as stone plate, the substrate table being movable over a top surface of the base plate, for example carried by air bearings, the top surface defining an X-Y horizontal plane. An Y-beam, extends along the X-direction. Movement of the Y-beam in the Y direction provides for a course positioning (i.e. a long stroke) of the substrate table in Y-direction. An X-motor is provided at the Y-beam, in order to move the substrate table in X-direction along the Y-beam, thereby providing a coarse positioning (i.e. a long stroke) of the substrate table in the X-direction. A fine positioning is provided by short stroke actuators that move the substrate table in respect of the X-motor. A performance in terms of maximum bandwidth of such configuration is largely limited by a stiffness of the Y-beam: resonances occurring in the Y-beam may limit a maximum performance in terms of acceleration, settling time, etc.
A second type is disclosed in WO01/18944 A1 which is enclosed herewith in its entirety by reference. In this configuration, the substrate table moves over a magnet plate, the magnets in combination with coils provided in the substrate table allow an actuation of the substrate table in 6 degrees of freedom. Although this configuration has many benefits, such as allowing to operate in vacuum (no air bearings to support the substrate table required), disturbance forces and disturbance torques on other parts of the lithographic apparatus may occur as the magnet plate in combination with the coils in the substrate table may result in propelling forces on the substrate table that are below a center of gravity of the substrate table.